This invention relates to a system for automatically controlling the index signal generation timing of a floppy disk drive unit.
Conventional floppy disk drive (FDD) units have an index pulse detector which produces a single index pulse upon every rotation of a magnetic recording medium (hereinafter referred to as a disk). This index pulse permits a floppy disk controller (FDC) to detect the start and end of a track on the disk.
According to 51/4 inch FDD units, for instance, an index hole is provided in advance and when the hole is detected by the index pulse detector coupled to a photoelectric sensor, the index pulse is produced. No index hole is provided in a 3.5 inch disk and the disk and a spindle motor are chucked at a constant angle so that a spindle is provided with a signal generator, such as a magnet.
The rising of a delayed index pulse is adjusted in order to properly execute data read/write from the begining of a track for providing a compatibility between FDD units. In this case, a positional difference between the index pulse and delayed index pulse is called an index positional accuracy. Conventionally, to attain the proper index positional accuracy, the mounting position of a sensor is adjusted for a 51/4 inch FDD unit while the rising of the delayed index pulse is electrically delayed for a 3.5 inch FDD unit. These adjusting systems utilize a CE (customer engineer) disk and the delay time is controlled by varying a resistor and a capacitor of a timer unit.
In either system, it is difficult to provide automatic index adjustment and high adjusting accuracy, and there is a strong demand for a system that fulfills the need.